Glass fiber strand is typically formed by attenuating filaments through bushing tips located at the bottom of a heated bushing containing molten glass. Often, the filaments are sprayed with water or other cooling fluid as they emerge from the bushing to quench them. The filaments are then passed over the application surface of an applicator where they are coated with a binder and/or size. After leaving the applicator surface, the filaments are then gathered into a unified strand in a gathering means, such as a gathering shoe, which is normally a grooved wheel or cylinder which is formed of a material which is not easily abraded by the filaments, such as graphite or brass. In some instances, the application and gathering steps are combined into a single operation, as in pad applicators.
The strand leaving the gathering means can then be handled in any of numerous ways. Often, the strand is passed across the face of a rotating spiral and is traversed by the spiral and collected on a rotating drum or collet as a forming package. In another operation, the strand is carried across the face of the rotating collet by means of a traversing guide eye. These two operations normally form either a generally barrel-shaped or cylindrical forming package.
Continuous strands can also be collected in a container. In this operation, the strand is passed between rotating wheels or belts or a combination of wheels and belts and is attenuated into a container. Glass strand may also be chopped between a wheel having a plurality of blades on the periphery thereof and a back-up wheel as it emerges from the gathering means and collected in a container or a chopped strand.
In the above operations, the collet, the belt and/or wheel attenuator or the chopper provides the necessary attenuative forces on the strand to attenuate the strands and the filaments associated therewith through the bushing.
One of the problems encountered in forming glass strand is control of the thermal environment below the bushing. The ability to form high quality glass filaments successfully relies, in large measure, on the control of the viscosity of the glass. Glass viscosity varies inversely with temperature, i.e. increases in temperature decrease the viscosity of the glass and vice versa. Only within small ranges of glass viscosity can glass filaments with consistent diameters be formed successfully.
As careful viscosity control of the glass is imperative, careful control of the thermal environment at and below the bushing is extremely important to control this viscosity. For the most part, bushing temperature control is maintained by regulating electrical energy input to the bushing, based upon temperature measurements of the bushing. However, while such control may regulate the temperature of the bushing itself, this control does not alone successfully regulate temperature in the fiber forming region below the bushing. Often, variations in temperature across the width and along the length of the bushing and below it are realized, due to the bushing tip pattern, airflow variations, and the like. A primary purpose of the present invention is to improve the environment of the fiber forming region below the bushing in a glass strand forming operation.
As previously mentioned, in the formation of glass strand it is often desired to quench the filaments immediately after they are formed by spraying them with water or other cooling fluid prior to their arrival at the application surface. Not only does this make for easier handling of the hot filaments by the operator, but it also aids in the solidification of the filaments and thus reduces changes of the filaments breaking as they are attenuated. While liquid cooling fluids have been used in the past to cool the filaments as they emerge from the bushing, no use has been made of liquid cooling fluids to aid in controlling the bushing environment. It is thus another purpose of the instant invention to make use of cooling fluids normally present in a glass fiber forming operation to assist in controlling the bushing environment.
It is also an object of the instant invention to provide cooling to various apparatus elements present in the fiber forming region below the bushing.
It is also an object of the instant invention to create a radiation shield encompassing the fiber forming region below the bushing to absorb radiant heat from this region and thus substantially reduce transfer of this heat from the fiber forming region to the environment immediately below the bushing, thus improving the comfort of the operator in the fiber forming position.